Coronavirus Likely Circulated Quietly For Months Before Wuhan Outbreak
Scientists have long known the coronavirus that causes COVID-19 circulated undetected in China before it reached the now-famous Huanan Seafood Wholesale Market in Wuhan in late December 2019 and kicked off the present pandemic.
New research in the journal Science offers some clues regarding that early quiet period.
In a two-pronged approach, researchers built a timeline based on how long SARS-CoV-2 takes to develop mutations, then cross-referenced their estimates with an epidemiological model of Wuhan to get a sense of the virus's history and earliest ancestor.
"But what we were interested in was whether there was a kind of a fuse that was burning before that ancestor and so in other words was the true index patient — the very first person with this virus in Wuhan." said co-author Michael Worobey, head of the Department of Ecology and Evolutionary Biology at the University of Arizona.
Worobey and his colleagues found the virus likely existed at low levels by early November 2019 and possibly as early as October.
Moreover, in about 70% of their simulations, the virus went extinct by itself instead of starting a pandemic — a result Worobey described as "extraordinary."
"To think that, if things had been just slightly different — if one person hadn't chosen to go to some area or event that caused a lot of transmission, if no one had brought that virus to that market — SARS-CoV-2 might not have gained a foothold, and we might not even know it existed," he said.
The results show how a virus's fate can hinge on conditions, like a carrier reaching an urban environment or joining a superspreader event.
They also underscore the difficulties involved in heading off new pathogens before they erupt into pandemics.
"It's just really hard, even once a virus like SARS-CoV-2 starts circulating in the population, to catch it early on, because there are so few people infected until it catches a lucky break," said Worobey.
And then it's too late.
"We've got to really step up our game if we want to do better with the next SARS-CoV-2-like outbreak," said Worobey.